When liquid is to be added to a certain level within a container, particularly opaque containers, trouble is often experienced in determining when the flow of liquid into the container should be stopped to prevent the container from overflowing. This is particularly true when a liquid such as battery acid (sulfuric acid) is to be added to a new lead-acid battery of the conventional type. Battery acid, as is known, is highly caustic and care should be taken to prevent contact of the acid with the skin or clothing. When acid is introduced into a battery through a funnel or by means of a dispenser or the like, it is difficult, without periodically stopping to examine the liquid level, to see how full the battery has become. Such periodic examination requires the funnel or dispenser to be removed, with concurrent dripping and messiness and wastage of time. These problems are compounded by the fact that lead-acid storage batteries ordinary have a number of compartments, each of which must be filled separately.
A device which would enable a battery to be filled with acid and would provide a continuing visual indication as to whether the battery acid has reached a given level without requiring removal of the device would greatly reduce the amount of time required to fill batteries and would reduce or eliminate hazardous contact of skin or clothing with the battery acid during the filling operation.